Return the sum of the array elements over the given axis.
Masked elements are set to 0 internally.

Parameters :

axis : {None, -1, int}, optional

Axis along which the sum is computed. The default
(axis = None) is to compute over the flattened array.

dtype : {None, dtype}, optional

Determines the type of the returned array and of the accumulator
where the elements are summed. If dtype has the value None and
the type of a is an integer type of precision less than the default
platform integer, then the default platform integer precision is
used. Otherwise, the dtype is the same as that of a.

out : {None, ndarray}, optional

Alternative output array in which to place the result. It must
have the same shape and buffer length as the expected output
but the type will be cast if necessary.

Returns :

sum_along_axis : MaskedArray or scalar

An array with the same shape as self, with the specified
axis removed. If self is a 0-d array, or if axis is None, a scalar
is returned. If an output array is specified, a reference to
out is returned.